Weird happenings! 1965 Johnson 9.5 HP - Motor cover stalls engine.

[onepyramid]

First of all, I know this motor was rebuilt by a guy that is truly trusted and works wonders on outboards. After seven years in the basement, this motor fired on the second pull.

Now, having said that...with the motor cover off, it idles fine, it revs fine, reaches WOT fine, comes back down and will purr at idle. It will do this all day long, UNTIL I try to put the motor cover on....then it bogs down, as if it is being choked to death. If I do this while it is at idle, it dies. If done at half throttle, it dogs down by several hundred rpm and runs rough as a cob...and then eventually sputters and dies.

I thought it might be air starvation, but I cannot see any way that can be true. Nothing on the inside of the cover is blocking the throat of the carb. I can put my hand nearly all the way over the throat of the carb (with the cover off) and get no similar results...plus there would have to be enough air inside this cover to feed that small carb for quite awhile....and these bogging down results are immediate.

I can see no wires, or anything else for that matter, that are anywhere close to where the cover sits. Everything in the electrical circuit was new...plugs, points, plug wires, etc.

I am flummoxed. Any ideas???

 

[F_R]

No reason to be flummoxed. That is a very common and well known problem with the 9.5 motors. Exhaust gasses are coming up inside the cover and it is breathing it's own stink. Much has been written on the subject. There are several routes the exhaust may be leaking from. Some are major repair projects.

My first question for you is: Are you running it in a tank? They will not run properly in a tank with the hood on, even when brand new.

 

[onepyramid]

No, it is mounted to the back of the runabout. I did run it in a 55 gallon drum, early on, but without the cover.

So where do I look?

And thank you.

 

[F_R]

1. There is a rubber flap seal about half way down, between the inner and outer housings that people are quick to blame. But it usually is not the culprit.

2. There is a seal on top of the water pump housing. Leave it out and the motor will smother itself to death. Likewise a spacer tube if it happens to be a long shaft. These parts often get left out when somebody does a water pump job.

3. Worst case scenario: There is a bellows seal around the upper shift rod and water tube. It is real flimsy material, often ripped. If it is ripped or torn, it will also smother itself to death. Terrible job for a novice to tackle. Many pros won't touch it either. This also applies to #1

4. And finally, it could be a leak under the hood, for instance the bellows exhaust relief outlet tube. You should be so lucky, hah.

 

[onepyramid]

Thanks. I will start looking to see what I can find.

 

[scout-j-m]

As someone with experience with this issue....do check #2 and #4 from what FR mentioned first. I ordered a new shift rod boot and took my motor apart to try to replace it and it has sat apart on my workbench for almost a year. Not saying that still isn't my issue, but it was a pain to take that motor apart and honestly I ma not sure how to get it all together lol.

 

[Crosbyman]

do searches on the issue on utube or google ... pretty certain I saw a video on the issue some time ago ...

 

[onepyramid]

OK, got the boat out of the water and the motor back in my workshop.


The rubber flap seal (1. above), other than a bit dirty, seems to be sealing up fine. The exhaust boot (4. above) seems to be in good shape, too.

I guess I will see about the water pump seal next, as this seems to be the path of least resistance.

And hear is a bit of a weird happening. Having put the cover back on the motor last night, I simply forgot to remove it this afternoon before moving the boat (advancing age, probably). I primed the bulb and pulled the starter rope and it fired right up and idled nicely. I put it in gear and motored right over to the dock...to the trailer. About the time I reached to shut it off, I thought "hey, this seems to be running fine today".

Is there something about this problem that would allow a cold engine to run o.k., but not so much after it warms up?

As I said, I will do the water pump seal....probably more for m own piece of mind and to check the impeller. Then I will put it back in the lake and see what happens.

Thanks for all the help.

 

[F_R]

Well, let's see--grasping at straws and imagination here. If running at dead slow idle, the exhaust housing could be 1/2 full of water (exhaust not blowing it out). That could be acting as a water seal across the defective/missing parts.

 

[onepyramid]

I've thought of another way to overcome this problem, I think.

If I alter the fiberglass cover of the motor to create a fresh air intake for the carb (shouldn't be too difficult based on the orientation of the intake near the top of the cover), wouldn't that eliminate the possibility of drawing in the foul exhaust from the motor enclosure?

 

[F_R]

You wouldn't be the first one to cut a hole above the carburetor intake. Don't leave it out in the rain though.

 

[TN-25]

I have a 1967 Johnson 9? that I got to replace the 1965 9? dad bought new and later gave away. Before I bought my 67 I gave it an idle test with the cowl on and off. I was satisfied when it made no difference either way. Later I noticed on my 67 that there is a tiny hole drilled into the starboard side of the lower motor cover. I thought it was a sneaky Micky Mouse fix added by a mechanic, but after looking at newer 9? they all had it as well. Evidently OMC was aware of the stalling problem during trolling or idling due to oxygen depletion in the surrounding spent exhaust gas. DON'T cut a hole in your cowl, but do consider a tiny hole in the starboard side of the lower shroud that OMC used as a fix. See picture below for the factory hole location on all post-66 9? motors. It can be done to earlier motors (64-66).

See the attached picture to see the tiny relief hole that OMC added to the 9? starting with the 1967 models. The hole is small enough to allow air to come in via least resistance, but not too large as to allow water to come in and noise to come out.

 

[scout-j-m]

I've thought of another way to overcome this problem, I think.

If I alter the fiberglass cover of the motor to create a fresh air intake for the carb (shouldn't be too difficult based on the orientation of the intake near the top of the cover), wouldn't that eliminate the possibility of drawing in the foul exhaust from the motor enclosure?

A previous owner had done something similar to mine where there were many small holes drilled into the cowling right above the carb throat. May have helped at some point but it is not enough to alleviate it entirely now. What it really needs is some type of intake that seals around the carb and goes out the cowl